Percutaneous transluminal coronary angioplasty (PTCA) is used to increase the lumen diameter of a coronary artery partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. Typically a first guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the first guidewire to a point just proximal of the stenosis. The first guidewire is then removed. A balloon catheter on a smaller 0.014 inch diameter second guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The second guidewire is advanced into the stenosis, followed by the balloon on the distal end of the catheter. The balloon is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. It has also been shown that the use of intravascular stents can measurably decrease the incidence of restenosis after angioplasty thereby reducing the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel reclosure. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in diameter from small coronary vessels of 3 mm or less to 28 mm in the aortic vessel. The invention applies to stent delivery systems for acute and chronic closure or reclosure of any body lumen.
A typical stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A typical stent ranges from 5 mm to 50 mm in length. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. Stents radially expand as the balloon is inflated, forcing the stent into contact with the interior of the body lumen thereby forming a supporting relationship with the vessel walls.
The biocompatible metal stent props open blocked coronary arteries, keeping them from reclosing after balloon angioplasty. In a typical prior art procedure a balloon of appropriate size and pressure is first used to open the lesion. The process is repeated with a stent crimped on a second balloon. The second balloon may be of higher pressure, e.g., more than 12 atmospheres, to insure that the stent is fully deployed upon inflation. The stent is deployed when the second balloon is inflated. The stent remains as a permanent scaffold after the balloon is withdrawn. The stent must be forced against the artery's interior wall so that it will fully expand thereby precluding the ends of the stent from hanging down into the channel encouraging the formation of thrombus.
Various shapes of stents are known in the art. U.S. Pat. No. 4,886,062 to Wiktor for "Intravascular Radially Expandable Stent and Method of Implant" discloses a two-dimensional zig-zag form, typically a sinusoidal form.
End caps to anchor the proximal and distal ends of stents are seen in U.S. Pat. No. 4,950,227 to Savin et al. for "Stent Delivery System, U.S. Pat. No. 5,108,416 to Ryan et al. for "Stent Introducer System", U.S. Pat. No. 5,443,495 to Buscemi et al. for "Polymerization Angioplasty Balloon Implant Device" and WO 96/31249 to Solar for "Non-Deformable Self-Expanding Parallel Flow Endovascular Stent and Deployment Apparatus Therefor".
Stent delivery systems using sheaths over the stents can be seen in U.S. Pat. No. 5,192,297 to Hull, U.S. Pat. No. 5,360,401 to Turnland et al. or U.S. Pat. No. 5,453,090 to Martinez et al.
U.S. Pat. Nos. 5,192,307 and 5,266,073 to Wall discloses coaxial catheters with the outer catheter being manipulated to urge the stent in place over the balloon. After the stent is over the balloon, the balloon will be inflated to urge the stent outwardly to its opened condition.
Stent delivery systems wherein the sheath is on the exterior of the stent are disadvantageous because such systems require the use of multiple balloon catheters which is costly and requires more operator time. Stent delivery systems with exposed stents without end caps are disadvantageous because the proximal or distal end of the stent may snag during delivery or retraction.